The present application relates to a prosthesis for femur replacement surgery and more particularly to a prosthesis which receives a modular neck assembly selected for a desired neck length, neck angle, anteversion and offset.
Surgery to replace the femur in total joint surgery involves the insertion of a stem in a cavity formed in the femur. The end of the stem extending from the cavity has a neck which is formed at an angle and the neck is mated with a socket in the hip. Every patient requires individual fitting due to the unique anatomical requirements of the particular patient. A prosthesis in which the stem and neck are a unitary device requires that the surgeon have a large quantity of prostheses available to provide a correct bio-mechanical function of the prosthesis with the patient. It is very costly to maintain a large inventory of prostheses and, despite the number of prostheses available, quite often the appropriate size and angle are not completely met.
More recently, modular prostheses have been designed to overcome this longstanding problem. The modular designs have each focused on a different aspect of the prosthesis. U.S. Pat. No. 4,919,670 to Dole et al disclose a tapered cylindrical lock mechanism disposed on the proximal end surface of the stem and the head mechanism including a complementary tapered aperture for receiving the cylindrical lock mechanism in a rigid mechanical coupling engagement. In U.S. Pat. No. 4,995,883, Demane et al disclose a modular hip prosthesis which can be custom fitted to a patient before surgery. A plurality of prostheses bodies, pads, heads, collars and extension sleeves are offered in various sizes. An elongated bolt extends through the prosthesis body and is connected to the extension sleeve. Luman, in U.S. Pat. No. 5,002,578 discloses a modular hip stem prosthesis apparatus which includes a hip stem with an integral, enlarged shoulder and a neck section mountable to the hip stem which are releasably interconnected with a bolt. The annular relation between the side arm and the longitudinal axis of the hip stem is selectively predetermined. In U.S. Pat. No. 5,002,581, Paxson et al disclose a modular hip joint prosthesis with adjustable angular variation. This variation is made possible by having the axis of the connection part of the stem and neck being angularly offset from the axis of the body of the stem and neck, respectively. Pappas et al, in U.S. Pat. No. 5,030,234 disclose a modular stem prosthesis which has a stem connected to an extension with a slip fit interconnection. Engagement between the stem and the extension is provided by deflectable end portions of one component of the prosthesis which are engaged in a mating deformation with the other component. Fallin, U.S. Pat. No. 5,108,452, is a continuation-in-part of Demane et al and discloses removable pads attached to the prosthesis body with a wedge to lock the connection between the prosthesis and the hip joint. In U.S. Pat. No. 5,286,260, Bolesky et al disclose a modular hip prosthesis for replacement of a portion of the femur comprising a kit that includes an upper and lower portion. A neck member is also provided to rigidly attach the head member to the body member. McTighe et al in U.S. Pat. No. 5,653,765 discloses a modular hip stem prosthesis having a neck member extending angularly outward from the shoulder peice and configured to receive a spherical hip ball for insertion into the hip socket. A locking screw secure joins the shoulder piece with the stem.
A further complication in the total joint surgery to replace the femur is that clinically, the metal of the prosthesis is not compatible with the bone on a modular scale. The different moduli of the bone and the metal causes a stress path to pass through the more rigid material and the stress between the bone and metal occurs distally shielding the proximal femur from stress. This results in atrophy of the proximal femur and pain to the patient and eventually, possible failure. To alleviate this problem, Averill et al in U.S. Pat. No. 4,888,023, disclosed a prosthesis with a fixation resistant finish on the external peripheral surface of the distal tip. The distal tip is selectively removable and replaceable. In U.S. Pat. No. 4,892,546, Kotz et al disclose an adjustable prosthesis for a joint bone having an elongated inner sleeve and an outer sleeve. The inner sleeve is telescopically slidable within the outer sleeve but is not rotatable. The inner sleeve includes a threaded spindle nut and a threaded spindle which are positioned within the inner sleeve. In U.S. Pat. No. 5,057,101, Dorr et al disclose a femoral prosthesis with a centering sleeve wherein the sleeve is removably attached midway along a stem of the prosthesis. Removable sleeves are disclosed.
Montagne in European Patent No. 0 201 407 A1 discloses a prosthesis with connecting members which are adjustable with an octagonal fitting. A sleeve is not disclosed on the shank of the prosthesis. Frey in European Patent No. 0 187 903 A1 discloses an adjustable hip joint prosthesis with an outer sleeve having an inner polyethylene liner. The outer sleeve has an outer surface with self-tapping threads to be screwed to the femur. In WIPO publication WO 94/07438, Tronzo discloses a bearing mechanism built into a femoral component which has a sleeve. The sleeve is disposed at the distal portion of the stem and buttresses a bearing retaining shoulder. Walker in WIPO publication WO 91/03992 discloses a prosthesis with a plastic sleeve having a non-uniform bore.
Despite the recognition and activity directed to solving these longstanding problems, none of the above-identified patents have been widely accepted and prostheses based on these references have not made a significant impact in the field. The problem still exists.